This invention relates to couplings for metal tubing or pipe. More particularly, this invention relates to structures for joining metal raceways employed in the installation of electrical conduits. Examples of such metal raceways are those defined in the National Electrical Code at Article #345 -- "Intermediate Metal Conduit" and at Article #346 -- "Rigid Metal Conduit."
Often it occurs during the installation of electrical conduits that offset rigid metal raceways or conduits must be employed and joined in order to complete a conduit run. Because of the offset in the conduits, the conduits cannot simply be rotated about a single longitudinal axis and thereby threaded into opposite ends of a common straight coupling. Another problem commonly arising, particularly where a conduit run is being broken into, is the need to join two conduits neither of which can be turned about its longitudinal axis.
In both of the foregoing situations, two types of couplings are commonly employed. One type of coupling is a split coupling, having two pieces which are placed over the point of junction of the two conduits and four bolts with nuts which interconnect the two pieces. The second type of coupling is commonly called the "Erickson" coupling and has three portions. A first sleeve, having an interior flange and an interior threaded surface, is slipped over the end of one of the conduits, and a second sleeve is threaded onto the end of the same conduit. A third sleeve, having an interior threaded surface and an exterior flange and threaded surface, is threaded onto the end of the second conduit. The first sleeve is then slipped back along the first conduit, over the second sleeve, and threaded onto the third sleeve, a tight coupling being obtained when the first sleeve is threaded against the exterior flange of the third sleeve and the second sleeve abuts against the interior flange of the first sleeve.
Both of the aforementioned types of coupling are comprised of a large number of parts, which parts can easily be misplaced on a job site. Also, both of the couplings are time-consuming to employ and are particularly awkward to use where there is tiering of conduits, multiple levels of conduit installed and closely spaced. The "Erickson" coupling requires the use of a large pipe wrench, and the split coupling the use of two open-end wrenches, for installation, and space limitations therefore can severely impair the efficiency with which these couplings may be employed.